1. Field of the Invention
The present invention relates to a rotor of a magneto generator for generating electricity under the action of electromagnetic induction produced between magnets and an armature winding by rotation of a flywheel.
2. Description of the Related Art
In an internal combustion engine, engine crank angle information and engine rotational speed information are required when controlling an ignition timing, a fuel injection time, and the like. Therefore, for example, as disclosed in Japanese Unexamined Patent Publication No. 2003-274601, when a flywheel magnet rotor is used as a rotor of a magneto generator, there is known a configuration in which an inductor magnetic pole portion made of protrusions is provided on the outer circumference of a peripheral wall of the flywheel so that the inductor magnetic pole portion is used to generate pulses including crank angle information and rotational speed information by a pulser (signal generator). In addition, the same publication discloses that the inductor magnetic pole portion is formed by punching out a part of the peripheral wall of the flywheel from the inner side to the outer side; and in order to correct an imbalance in mass due to protrusions of the inductor magnetic pole portion on the outside, a concave portion is formed on the inside of the inductor magnetic pole portion and a correction weight for the imbalance in mass is provided.
FIGS. 3A to 3C and FIGS. 4A to 4C are views showing other known examples, in each of which a protrusion portion (inductor magnetic pole portion) is formed on a peripheral wall of such a flywheel, for showing a known magneto generator to be objected in the present invention. First, FIG. 3A shows a front view; FIG. 3B shows a partial cross-sectional side view; and FIG. 3C shows a partially enlarged view of FIG. 3B. Referring to FIGS. 3A to 3C, reference numeral 1 denotes a bowl-shaped (cup-shaped) formed flywheel; 2 denotes a plurality of magnets circumferentially arranged on the inner circumference of a peripheral wall of the flywheel 1; 3 denotes a magnet cover serving as a cylindrical guard ring closely fitted to the inner circumferential side of the circularly arranged magnets 2; and 4 denotes resin or molding material filled in gaps between the magnets 2, for integrally securing the magnets 2 and the magnet cover 3 to the flywheel 1.
A plurality of protrusions (also referred to as trigger pole hereinafter) 5 arranged at equally spaced intervals are formed on an outer circumferential surface of the flywheel 1; and, there is formed a toothless portion NT that is a place where a trigger pole 5 is partly lacked. The place where the trigger pole is lacked, that is, the toothless portion NT is a reference position; and, since the flywheel 1 is directly connected to a crankshaft of an engine, the rotation state of the flywheel 1 is the same as that of the engine. Therefore, the rotation state of the flywheel 1, that is, the rotation state of the engine can be confirmed by detecting the toothless portion NT with a signal sensor S.
In addition, presence of the toothless portion NT means that the flywheel is not kept in balance; and, in order to correct the imbalance, a balance correction hole is provided at a symmetrical position of the toothless portion NT on the outer circumferential surface of the flywheel 1.
Furthermore, there exists a boss 6 which is attached to a rotation shaft at the center in a sidewall of the flywheel 1; a key groove 7 is formed on the boss 6; and the key groove 7 and the toothless portion NT serving as the reference position of the trigger poles 5 are arranged to form a predetermined angle.
A stator 8 having an armature winding which is for generating electricity under the action of electromagnetic induction produced with the magnets 2 by the rotation of the flywheel 1 is formed on the inner circumferential side of the flywheel 1. The stator 8 includes a magneto coil (armature winding) 8c wound to a laminated core made of a plurality of thin steel sheets. Insulating material (for example, resin mold and epoxy system powder coating) which is for ensuring insulation with respect to the magneto coil 8c is applied to the laminated core; and an armoring process (varnish, epoxy resin, and the like) which is for ensuring rigidity and insulation quality is applied to the magneto coil 8c. 
In addition, FIG. 4A to 4C are views showing a known example in which a plurality of trigger poles 5 are punched out in an axial direction of the magneto generator.
In such known flywheel magneto generators, the trigger poles 5 are protrusions, each of the trigger poles being formed by punching out from an inner circumferential surface to an outer circumferential surface of the flywheel 1; and therefore, a good deal of process and time are required for manufacturing the trigger poles. In addition, there exists a place (toothless portion NT) where one protrusion is lacked with respect to the protrusions 5 arranged at equally spaced intervals, and the balance correction hole is formed at the symmetrical place with respect to the toothless portion NT; however, as for a forming process of the balance correction hole, a process different from a protrusion punching-out process is required.
Furthermore, in the method which punches out the protrusions 5 from the inner circumferential surface to the outer circumferential surface of such flywheel 1, roundness of the inner circumferential surface of the flywheel 1 is degraded and it is difficult to ensure inner diameter accuracy of the flywheel 1.
Besides, formation of the trigger poles 5 of the flywheel 1 can be performed by a cutting-out method different from the punching-out method; however, in the cutting-out method, cutting-out is necessary for each protrusion; and accordingly, longer time in manufacturing time is required.
Further, in the structure in which the trigger poles 5 are punched out in the axial direction, there arise drawbacks in that it is large in the number of components; an air gap g between the signal sensor S and the trigger pole 5 is unstable by summation tolerances of the respective components; and a variation in signal is concerned.